Just to review.. SOMI is of course Sea of Moving Ice. Its the area associated with Mod 10.5.
This shows treasure map locations.
Less useful for the campaign but still fun, the map of fishing spots and their names. This is used to finish out your fish collection. Check each of the fish in your collections tab ('ctrl-j') and look up the name of where its found on this map.
Elynaen recommends this map: https://imgur.com/a/ZV5Z8#3sPH6om